The invention relates to an antenna, preferably operable in the micro wave range, comprising a Luneberg lens. The lens in the form of a round disc-shaped element, for example of dilectric material, having a radially varying reflection index. The lens is covered on at least one of its plane sides by a conducting plane. Feeders are distributed around the circumference of the lens for transmitting and receiving electromagnetic energy passing through the lens and emerging from or entering into, respectively, the part of the circumference of the lens situated opposite an active feeder.
Known antennas of this kind are either constructed for polarization of the E-vector perpendicular to the plane of the lens or polarization of the E-vector in the plane of the lens. If the lens is oriented horizontally, as is usually the case, the former polarization can be called vertical and the latter horizontal.
A problem with such an antenna, where the whole lens circumference is surrounded by feeders, is that the radiation transmitted from or received by each individual feeder must pass through the diametrically opposed feeder, which attenuates the radiation. In other words, the diametrically opposed feeder "hides" the transmitting/receiving feeder. Each feeder must therefore present a small geometric projection surface, as seen in a plane perpendicular to the propagation direction of the radiation in the lens. Besides the geometric extension in a plane perpendicular to the propagation direction for a given wave, it is also possible to define for each feeder an "effective antenna area" in the plane, which must also be small so that the feeder is not "hidden". This effective antenna area depends i.a. on the load impedance of the feeder and can be varied by electrical switching operations.
In known lens antenna constructions with feeders distributed around the circumference thereof only one single feeder is active at a time. Those feeders which have a hiding effect on the active feeder can be switched electrically so that the effective antenna areas thereof will be small. These switched feeders cannot of course, be used either as receiving or transmitting elements as long as they must have a small hiding influence on the active feeder.